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   <title>KDbg - User's Manual - Type Tables</title>
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<p><a href="index.html">Contents</a></p>
<h1>
KDbg's Type Table</h1>
<p>KDbg can display a short description of structured types, so
that it is not necessary to expand the variable in the <a href="localvars.html">local
variables window</a> or <a href="watches.html">watched expressions window</a>.
The information which member variable is displayed is stored in <em>type
tables</em>. There is generally one type table per shared library.</p>

<p>KDbg's default type tables are located under <tt>$prefix/share/apps/kdbg/types</tt>.
User defined type tables can be placed in <tt>${KDEHOME}/share/apps/kdbg/types</tt>, where
<tt>${KDEHOME}</tt> is <tt>~/.kde</tt> if it is not a defined environment variable.
The file names end with <tt>.kdbgtt</tt>. Example: The type table for <tt>libqt.so</tt>
is named <tt>qt.kdbgtt</tt>.
User defined type tables override the type tables provided by the system.</p>
<p>A type table file obeys the regular KDE configuration file syntax. The
file has the following groups:</p>
<ul>
<li>
A group <tt>[Type Table]</tt> which lists the types and information how
the debugger can identify whether the program is linked against the library.</li>

<li>
A group for each type which has information about how the value of such
a type is displayed by KDbg.</li>
</ul>
<p>In order to determine which type tables apply to the program being debugged
KDbg lists the shared libraries it is linked to. Then it matches the names
against the <tt>ShlibRE</tt> entries of all type tables. Those that match
are used. If a type appears in several type tables, it is unspecified which
one will be used.</p>
<p>KDbg's type recognition only works for libraries that are linked dynamically
to the program being debugged.</p>
<h2>
The <tt>[Type Table]</tt> group</h2>
<p>This group contains the following entries:</p>
<ul>
<li>
<tt>Types1</tt>, <tt>Types2</tt>, etc. These entries name the types,
separated by commas.
Each of the entries can list any number of types. The entries must be numbered
consecutively (KDbg stops reading at the first gap), although an entry may be
empty (i.e. contain no type at all).
Sometimes the order in which the names are listed is important
(see <tt>Alias</tt> types below).</li>

<li>
<tt>ShlibRE</tt>. KDbg uses this entry to determine if the type table applies
to the program being debugged. For this purpose KDbg determines the shared
libraries to which the program is linked. If any of the libraries matches
this entry, the type table applies. The entry is a <a href="http://doc.trolltech.com/4.0/qregexp.html#introduction">Qt regular
expression</a>.
Note that back-slashes must be doubled because the back-slash is an escape
character in the configuration file syntax.</li>

<li>
<tt>LibDisplayName</tt>. This entry is used in lists where the available
type tables are listed to identify this type table.

<br><font size=-1>This is not used currently.</font></li>

<li>
<tt>EnableBuiltin</tt> lists extensions that must be enabled if this
library is used. Currently, two builtins are supported:
<ul>
<li>
<tt>QString::Data</tt> is used to display unicode strings of Qt's <tt>QString</tt>
class. See below.</li>
<li><tt>QCharIsShort</tt> is used only in connection with <tt>QString::Data</tt>
to specify that a unicode character is stored in an object of type <tt>short</tt>.
See <tt>qt3.kdbgtt</tt> for examples.</li></ul></li>
</ul>

<p>In the case of regular types the names of types should follow the output of the
<tt>whatis</tt> gdb command less any <tt>const</tt>, <i>spaces</i>, or trailing
<tt>&</tt>.
If the type contains a a comma in its name, it must be escaped with a backslash.
But note that the comma should not be escaped in the type's group (which is described
in the next section).
</p>
<p>In the case of template types the name can be arbitrary because the type's group
will mention the template name and a type parameter list.</p>

<h2>
The type's group</h2>
<p>There is one group for each type that is named exactly as the type.
Each group contains the following entries:</p>
<ul>
<li>An optional <tt>Template</tt> entry that specifies the exact template type
name as it is reported by gdb's <tt>whatis</tt> command. However, it is
possible to replace template parameter types at the top-most level by an
asterisk&nbsp;<tt>*</tt>, which acts as a wildcard: It matches <b>one</b>
template type argument that is reported by <tt>whatis</tt> (except that an
asterisk in the last position matches all remaining template type arguments).
</li>
<li>
<tt>Display</tt> determines how the value of the type is displayed by KDbg.
The string must contain 1 to 5 percent characters '<tt>%</tt>'. These are
replaced by the results of the expressions printed by the <tt>Expr</tt><i>x</i>
entries.</li>

<li>
One or more of <tt>Expr1</tt>, <tt>Expr2</tt>, etc. Each of them must contain
one or more <tt>%s</tt> sequence, which will be replaced by the expression
whose value is investigated. The so constructed expression is submitted
to gdb, and the result substituted back for the corresponding percent character
in the <tt>Display</tt> string.</li>

<li>
An optional <tt>FunctionGuard</tt><i>x</i> that is associated with the corresponding <tt>Expr</tt><i>x</i>.
If the evaluation of the resulting gdb expression returns an error, the corresponding expression from <tt>Expr</tt><i>x</i> is not evaluated. (This is used to guard function calls.)
<li>
<tt>Alias</tt> names an alias type. If this entry is present, the type
is treated like the specified type. That alias type must appear before
this type in the <tt>Types</tt><i>x</i> entries in the <tt>Type Table</tt>.</li>
</ul>
<p><font size=-1>Currently the number of expressions per type is limited to
5. This can easily be changed if it's too restrictive, but I recommend
not to go to that limit at all - it will slow down the debugging process.</font></p>
<p>KDbg recognizes a special extension that is used to display Qt 2.x's and Qt 3.x's
unicode strings: If an <tt>Expr</tt><i>x</i> is prepended with <tt>/QString::Data</tt>,
it is assumed that the result of the expression is a pointer to a <tt>QString::Data</tt>.
The value displayed is the unicode string that this instance of <tt>QString::Data</tt>
represents (which can be <tt>QString::null</tt> if it is Qt's well-defined
null string or <tt>(null)</tt> if the <tt>unicode</tt> member is the null
pointer). See <tt>qt2.kdbgtt</tt> for examples.</p>
<p>Tip: It is not necessary to define derived types if they ought to be
treated the same as the base class - KDbg can deduce derived types and
uses the type specification of the (leftmost) base class. You can use the
<tt>Alias</tt>
entry to quickly specify that a type should be treated like a non-leftmost
base class for a multiple-inheritance class.</p>
<h2>
An example</h2>
<p>The example shows how <tt>QString</tt> and <tt>QRect</tt> are defined
in <tt>qt3.kdbgtt</tt>. Furthermore, the template type <tt>QValueVector</tt>
is defined. This example applies to Qt 3.x, which is located in shared library
whose name ends in <tt>libqt-mt.so.3</tt>.</p>
<pre>[Type Table]
Types1=QString,QRect
Types2=QValueVector
LibDisplayName=libqt 3.x
ShlibRE=libqt-mt\\.so\\.3$
EnableBuiltin=QString::Data,QCharIsShort

[QString]
Display={ % }
Expr1=/QString::Data (%s).d

[QValueVector]
Template=QValueVector<*>
Display={ size=% shared=% capacity=% }
Expr1=($tmp=(%s).sh)->finish-$tmp->start
Expr2=(%s).sh->count
Expr3=($tmp=(%s).sh)->end-$tmp->start

[QRect]
Display={ tl=(%,%) br=(%,%) }
Expr1=(%s).x1
Expr2=(%s).y1
Expr3=(%s).x2
Expr4=(%s).y2</pre>
<p>This example shows these features:</p>
<ul>
<li>The name of the template type, <tt>QValueVector</tt> is irrelevant.
The exact type name is specified under the <tt>Template=</tt> entry.
It specifies a single wildcard so that it applies to all specializations.
</li>
<li>In order to evaluate the expression that was supplied in the <tt>%s</tt>
only once, the result is stored in a temporary gdb variable and reused later in
the same expression.</li>
<li>Note that it is safer to wrap the <tt>%s</tt> in parentheses.</li>
</ul>
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